Magnetic Field Sensors and Methods for Fabricating the Magnetic Field Sensors

ABSTRACT

Magnetic field sensors and associated methods of manufacturing the magnetic field sensors include molded structures to encapsulate a magnetic field sensing element and an associated die attach pad of a lead frame and to also encapsulate or form a magnet or a flux concentrator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. patentapplication Ser. No. 13/241,380, filed Sep. 23, 2011, which applicationis a Divisional application of U.S. patent application Ser. No.12/328,798, filed Dec. 5, 2008, which applications are incorporatedherein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to magnetic field sensors, and, moreparticularly, to magnetic field sensors having a magnetic field sensingelement die and magnet and also to the assembly and packaging of themagnetic field sensors.

BACKGROUND OF THE INVENTION

Magnetic field sensors in the form of so-called “proximity detectors”that can detect the presence of a ferromagnetic object proximate to themagnetic field sensor are known. Proximity detectors typically include apermanent magnet to generate a magnetic field and also include amagnetic field sensing element, for example, a Hall effect element, todetect changes in the strength of the magnetic field associated with thepermanent magnet as a ferromagnetic object moves through the magneticfield.

The output signal of a magnetic field sensing element is dependent uponthe strength of a magnetic field that the magnetic field sensing elementexperiences. Therefore, the magnetic field sensing element can detect adistance between the proximity detector and a ferromagnetic objectwithin the magnetic field generated by a permanent magnet. The rangeover which the ferromagnetic object can be detected is limited by theflux density, i.e., the strength of the magnetic field.

Where it is desired to determine the speed or rotational position of arotating object, such as a disk mounted on a shaft, the object can beprovided with ferromagnetic surface features, such as teeth, thatproject toward the proximity detector. The proximity of a tooth to theproximity detector tends to increase the strength of the magnetic fieldproximate to a proximity detector. Accordingly, by monitoring the outputof the proximity detector, the rotational speed of the disk can bedetermined by correlating the peaks in the output of the proximitydetector with the known number of teeth on the circumference of thedisk. Similarly, when the teeth are irregularly spaced in apredetermined pattern, the rotational position of the object can bedetermined by correlating the peak intervals with the known intervalsbetween the teeth on the disk.

One type of proximity detector uses a Hall effect element. The Halleffect element is typically mounted so that is has a maximum responseaxis directed toward the object to be sensed. The associated magnet ismounted in a position to achieve a magnetic field aligned generallyalong the maximum response axis of the Hall effect element. The objectto be sensed can be a high magnetic permeability component that can haveprojecting surface features, which increase the strength of the magnet'smagnetic field as the distance between the surface of the object and thepermanent magnet is reduced. While one form of object can be a gear,another form of object can be a segmented ring magnet. Yet another formof object does not rotate at all, but merely moves closer to or furtheraway from the proximity detector. The object to be sensed moves relativeto the stationary Hall effect element within the proximity detector, andin doing so, causes the magnetic flux through the Hall effect element tovary in a manner corresponding to the position of the object. With thechange in magnet flux, there occurs the corresponding change in magnetfield strength, which increases (or alternatively, decreases) the outputsignal from the Hall effect element.

It will be understood that, within an integrated proximity detector, aposition or spacing of the magnet relative to the magnetic field sensingelement, e.g., the Hall effect element, greatly influences thesensitivity of the proximity detector. Therefore, it is desirable thatthe spacing be close and that spacing be consistent device to device.

With the increasing sophistication of products, proximity detectors havebecome common in automobile control systems. Examples of automotiveproximity detectors include proximity detectors that detect ignitiontiming from a position of an engine crankshaft and/or camshaft, and theproximity detectors that detect a position or rotation and a speed ofrotation of an automobile wheel for anti-lock braking systems and fourwheel steering systems.

A common shortcoming of proximity detectors is their dependence upon thedistance, known as the air gap, between the object to be sensed and themagnetic field sensing element within the proximity detector. Morespecifically, as the air gap increases, the output of a Hall effectelement within the proximity detector, which is directly proportional tothe strength of the magnetic field, decreases, making it more difficultto accurately analyze the output of the Hall effect element.

Conventionally, the air gap is defined as a distance between the objectto be sensed and the outer surface of the package containing theproximity detector. However, as used herein, the term “effective airgap” is used to describe a distance between the object to be sensed andthe magnetic field sensing element, e.g., Hall effect element, withinthe packaged proximity detector.

Some forms of proximity detectors that package a magnet and a Halleffect element together are described in U.S. Pat. No. 5,963,028, issuedOct. 5, 1999, and U.S. Pat. No. 6,265,865, issued Jul. 24, 2001, whichare incorporated herein by reference in their entirety.

It is known that a magnet is relatively expensive. The manufacture ofconventional forms of proximity detectors does not allow the magnet tobe reused or replaced once the molding step is completed. Thus, if aconventional proximity detector fails manufacturing testing aftermolding, the cost of the magnet is lost in addition to the cost of thesemiconductor die and packaging materials.

It would be desirable to provide a packaging scheme for a proximitydetector (or magnetic field sensor) that would provide reliableprotection from the environment, that would avoid an excessive increasein the effective air gap between the associated magnetic field sensingelement and the object to be sensed, that would allow the magnetic fieldsensing element to be as close as possible to the magnet, and for whicha proximity detector that fails testing during manufacture need notresult in a loss of the magnet.

Other forms of proximity detectors include a magnet apart from anintegrated proximity detector. Other forms of magnetic field sensorsemploy no magnet at all, but instead sense an external magnetic fieldexperienced by the magnetic field sensor. All of these forms of magneticfield sensors would also benefit from the above characteristics.

SUMMARY OF THE INVENTION

The present invention provides magnetic field sensors and methods tomake the magnetic field sensors.

In accordance with one aspect of the present invention, a method offabricating a magnetic field sensor includes attaching a magnetic fieldsensor circuit die to a first surface of a die attach pad of a leadframe. The die attach pad has the first surface and a second opposingsurface. The method also includes forming a molded capsule enclosing themagnetic field sensor circuit die. The molded capsule includes a cavityhaving an inner cavity surface. A portion of the inner cavity surface isproximate to the second surface of the die attach pad. The cavity has ashape capable of retaining a liquid. The method also includes placing amagnet into the cavity and proximate to the second opposing surface ofthe die attach pad and placing a liquid encapsulant into the cavityproximate to the magnet. The method also includes curing the liquidencapsulate to a solid condition to retain the magnet.

In accordance with another aspect of the present invention, a magneticfield sensor includes a lead frame comprising a die attach pad. The dieattach pad comprises first and second opposing surfaces. The magneticfield sensor also includes a magnetic field sensor circuit die proximateto the first surface of the die attach pad and a molded capsuleenclosing the magnetic field sensor circuit die. The molded capsuleincludes a cavity having an inner cavity surface. A portion of the innercavity surface is proximate to the second surface of the die attach pad.The cavity has a shape capable of retaining a liquid. The magnetic fieldsensor also includes a magnet proximate to the second surface of the dieattach pad and disposed within the cavity. The magnetic field sensoralso includes a cured liquid encapsulant disposed within the cavity andconfigured to retain the magnet within the cavity.

In accordance with another aspect of the present invention, a method offabricating an integrated sensor includes attaching a magnetic fieldsensor circuit die to a first surface of a die attach pad of a leadframe. The die attach pad has the first surface and a second opposingsurface. The method also includes forming a molded capsule enclosing themagnetic field sensor circuit die. The molded capsule covers the secondsurface of the die attach pad forming an insulating layer over thesecond surface of the die attach pad. The method also includes placing amagnet over the insulating layer and forming a molded enclosuresurrounding the magnet.

In accordance with another aspect of the present invention, a magneticfield sensor includes a lead frame having a die attach pad. The dieattach pad has first and second opposing surfaces. The magnetic fieldsensor also includes a magnetic field sensor circuit die coupledproximate to the first surface of the die attach pad and a moldedcapsule enclosing the magnetic field sensor circuit die. The moldedcapsule covers the second surface of the die attach pad forming aninsulating layer over the second surface of the die attach pad. Themagnetic field sensor also includes a magnet coupled proximate to thesecond surface of the die attach pad so that the insulating layer isbetween the magnet and the second surface of the die attach pad. Themagnetic field sensor also includes a molded enclosure surrounding themagnet.

With the above arrangements, a packaging scheme for a magnetic fieldsensor provides reliable protection from the environment that avoids anexcessive increase in an effective air gap between the associatedmagnetic field sensing element and the object to be sensed, that allowsthe magnetic field sensing element to be as close as possible to themagnet, and that does not result in loss of a costly magnet if themagnetic field sensor fails during manufacturing testing.

In accordance with another aspect of the present invention, a method offabricating a magnetic field sensor includes attaching a magnetic fieldsensor circuit die to a first surface of a die attach pad of a leadframe, the die attach pad having the first surface and a second opposingsurface. The method also includes forming a molded capsule enclosing themagnetic field sensor circuit die. The molded capsule includes a cavityhaving an inner cavity surface. A portion of the inner cavity surface isproximate to the second surface of the die attach pad. The cavity has ashape capable of retaining a liquid. The method also includes placing aliquid material into the cavity and proximate to the second opposingsurface of the die attach pad. The liquid material is filled withferromagnetic particles to either generate a magnetic field or toconcentrate a magnetic field. The method also includes curing the liquidmaterial.

In accordance with another aspect of the present invention, a magneticfield sensor includes a lead frame comprising a die attach pad. The dieattach pad has first and second opposing surfaces. The magnetic fieldsensor also includes a magnetic field sensor circuit die proximate tothe first surface of the die attach pad and a molded capsule enclosingthe magnetic field sensor circuit die. The molded capsule includes acavity having an inner cavity surface. A portion of the inner cavitysurface is proximate to the second surface of the die attach pad. Thecavity has a shape capable of retaining a liquid. The magnetic fieldsensor also includes a cured liquid material disposed within the cavity.The cured liquid material is filled with ferromagnetic particles toeither generate a magnetic field or to concentrate a magnetic field.

In accordance with another aspect of the present invention, a method offabricating a magnetic field sensor includes attaching a magnetic fieldsensor circuit die to a first surface of a die attach pad of a leadframe. The die attach pad has the first surface and a second opposingsurface. The method also includes forming a molded capsule enclosing themagnetic field sensor circuit die. The molded capsule covers the secondsurface of the die attach pad forming an insulating layer over thesecond surface of the die attach pad. The method also includes forming amolded structure proximate to the second surface of the die attach pad.The molded structure is filled with ferromagnetic particles to eithergenerate a magnetic field or to concentrate a magnetic field.

In the above arrangements, the ferromagnetic particles can be eitherhard ferromagnetic particles that can generate a permanent magneticfield, or they can be soft ferromagnetic particles that can concentratea magnetic field.

In accordance with another aspect of the present invention, a magneticfield sensor includes a lead frame comprising a die attach pad. The dieattach pad comprises first and second opposing surfaces. The magneticfield sensor also includes a magnetic field sensor circuit die coupledproximate to the first surface of the die attach pad. The magnetic fieldsensor also includes a molded capsule enclosing the magnetic fieldsensor circuit die. The molded capsule covers the second surface of thedie attach pad forming an insulating layer over the second surface ofthe die attach pad. The magnetic field sensor also includes a moldedstructure proximate to the second surface of the die attach pad. Themolded structure is filled with ferromagnetic particles to eithergenerate a magnetic field or to concentrate a magnetic field.

With the above arrangements, a packaging scheme for a magnetic fieldsensor provides reliable protection from the environment that avoids anexcessive increase in an effective air gap between the associatedmagnetic field sensing element and the object to be sensed, and thatdoes not result in loss of a costly magnet if the magnetic field sensorfails during manufacturing testing.

In other words, the partially packaged magnetic field sensor can betested in manufacturing in a form for which it is possible to remove themagnet. This may be accomplished, for example, by first testing themagnetic field sensor using a magnet in the testing apparatus that ismagnetized and reused for various parts during testing. This allows theactual magnet in the final magnetic field sensor to only be placed intothe magnetic field sensor after the testing and only into a known gooddie assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIGS. 1-1C are cross sections that show a process flow for fabricating amagnetic field sensor in the form of a proximity detector;

FIGS. 2-2C are cross sections that show another process flow forfabricating another magnetic field sensor in the form of a proximitydetector;

FIGS. 3-3C are cross sections that show yet another process flow forfabricating yet another magnetic field sensor in the form of a proximitydetector; and

FIG. 4 is a top view showing fabrication steps for fabricating amagnetic field sensor, for example, the magnetic field sensor of FIGS.3-3C, and including a capacitor encased during one of the molding steps.

DETAILED DESCRIPTION OF THE INVENTION

Before describing the present invention, some introductory concepts andterminology are explained. As used herein, the term “magnetic fieldsensor ” is used to describe a circuit that includes a “magnetic fieldsensing element.” Magnetic field sensors are used in a variety ofapplications, including, but not limited to, a current sensor thatsenses a magnetic field generated by a current flowing in a currentconductor, a magnetic switch or “proximity detector” that senses theproximity of a ferromagnetic object, a proximity detector that sensespassing ferromagnetic articles, for example, magnetic domains of a ringmagnet or gear teeth, and a magnetic field sensor that senses a magneticfield density of a magnetic field.

While magnetic field sensing elements are shown and described below tobe Hall effect elements, in other arrangements, the magnetic fieldsensing elements can be, but are not limited to, Hall effect elements,magnetoresistance elements, or magnetotransistors. As is known, thereare different types of Hall effect elements, for example, a planar Hallelement, and a vertical Hall element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, an anisotropicmagnetoresistance element (AMR), a tunneling magnetoresistance (TMR)element, and a magnetic tunnel junction (MTJ).

Referring to FIG. 1, a method of fabricating a magnetic field sensorincludes attaching a magnetic field sensor circuit die 10, i.e. amagnetic field sensing element, e.g., a Hall effect element, to a firstsurface 12 ba of a die attach pad 12 b of a lead frame 12. The dieattach pad 12 b has the first surface 12 ba and a second opposingsurface 12 bb. The method can also include coupling the magnetic fieldsensor circuit die 10 to leads 12 a of the lead frame 12 with wire bonds14 or the like.

Referring now to FIG. 1A, in which like elements of FIG. 1 are shownhaving like reference designations, the method further includes forminga molded capsule 16 enclosing the magnetic field sensor circuit die 10.The molded capsule 16 can be made of a variety of materials, forexample, E670C mold compound from the Sumitomo Corporation, HYSOL® MG52Fmold compound from the Henkel Loctite Corporation, or PLASKON® CK-6100mold compound from Cookson Electronics. In some embodiments, the moldedcapsule 16 can be formed in a one step molding process. In someembodiments, the molded capsule 16 can be comprised of a single uniformmaterial. The molded capsule 16 can include a cavity 16 c having aninner cavity surface 16 ca. A portion of the inner cavity surface 16 cacan be proximate to or can include the second surface 12 bb of the dieattach pad 12 b. The cavity 16 c has a shape capable of retaining aliquid. In other words, the cavity can be surrounded by a rim 16 a, 16 cand can be open in only one area, which will be more fully understoodbelow from the discussion in conjunction with FIG. 1B.

Referring now to FIG. 1B, in which like elements of FIGS. 1 and 1A areshown having like reference designations, a liquid encapsulant 20 can bedeposited into the cavity 16 c. The liquid encapsulant 20 can be made ofa variety of materials, for example, HYSOL® FP4450 or FP4451 from theHenkel Loctite Corporation, CRP-3400 from the Sumitomo Corporation, orCircalok™ 6009 A/B from the Lord Corporation. The cavity 16 c can beopen to accept the liquid encapsulant 20, but otherwise enclosed by therim 16 a, 16 b to keep the liquid encapsulant 20 from leaving the cavity16 c.

Referring now to FIG. 1C, in which like elements of FIGS. 1-1B are shownhaving like reference designations, a permanent magnet 22 can be placedinto the cavity 16 c proximate to the second surface 12 bb of the dieattach pad 12 b, and can be essentially surrounded by the liquidencapsulant 20, since the liquid encapsulant deposited in FIG. 1B willtend to rise around the magnet 22 as it is immersed in the liquidencapsulant 20. Thereafter, the liquid encapsulant 20 can be curedeither at room temperature or at elevated temperature.

In some other arrangements, the magnet 22 is placed into the cavity 16 cbefore the liquid encapsulant 20, and thereafter the liquid encapsulant20 is deposited into the cavity 16 c to surround the magnet 22. In someembodiments, an insulating epoxy, for example a die attach epoxy, can beused to attach the magnet to the leadframe prior to application of theliquid encapsulant 20.

In some embodiments, an insulative material 30 can be disposed betweenthe magnet 22 and the lead frame 12, for example a glass filledmaterial, e.g., Dow Corning 7030 Die Attach Adhesive. Application ofthis material between the magnet 22 and the lead frame 12 can result inan accurate and repeatable separation between the magnet 22 and the leadframe 12, which would tend to result in magnetic field sensors withimproved unit-to-unit sensitivity consistency.

In some embodiments, the magnet 22 has a magnetic field orientedapproximately perpendicular to the first and second surfaces 12 ba, 12bb, respectively, of the die attach pad 12 b. In these embodiments, themagnetic field sensor circuit die 10 comprises a magnetic field sensingelement, for example, a Hall effect element, having a maximum responseaxis also approximately perpendicular to the first and second surfaces12 ba, 12 bb of the die attach pad 12 b.

In some other embodiments, the magnet 22 has a magnetic field orientedapproximately parallel to the first and second surfaces 12 ba, 12 bb,respectively, of the die attach pad 12 b. In these embodiments, themagnetic field sensor circuit die 10 comprises a magnetic field sensingelement, for example, a giant or anisotropic magnetoresistance element,having a maximum response axis also approximately parallel to the firstand second surfaces 12 ba, 12 bb of the die attach pad 12 b.

The above-described method results in a magnetic field sensor 24 havingthe lead frame 12 with the die attach pad 12 b, the die attach pad 12 bhaving the first and second opposing surfaces 12 ba, 12 bb,respectively. The magnetic field sensor circuit die 10 is proximate tothe first surface 12 ba of the die attach pad 12 b. The molded capsule16 encloses the magnetic field sensor circuit die 10. The magnet 22 isproximate to the second surface 12 bb of the die attach pad 12 b anddisposed within the cavity 16 c. The cured liquid encapsulant 20 isdisposed within the cavity 16 c and configured to retain the magnet 22within the cavity 16 c.

In some alternate embodiments, the magnet 22 is omitted. In theseembodiments, the liquid encapsulant 20 can fill the entire cavity 16 cand can be filled with magnetic particles to generate a permanentmagnetic field in place of the magnet 22. For, example the liquidencapsulant 20 can be an epoxy material filled with strontium ferriteparticles. These embodiments can also form a proximity detector.

In still some other alternate embodiments, the magnet 22 is also omittedand the liquid encapsulant 20 is filled with soft magnetic particles toform a magnetic field concentrator, or flux concentrator. For, examplethe liquid encapsulant 20 can be an epoxy material filled with NiZn orMnZn ferrite particles. These embodiments also form a proximity detectorif the object to be sensed generates a magnetic field. However, theseembodiments can also form a magnetic field sensor used for otherapplications.

Referring now to FIGS. 2-2C, in which like elements of FIGS. 1-1C areshown having like reference designations, but wherein a molded capsule16′ is different than the molded capsule 16 of FIGS. 1-1C, a magneticfield sensor 26 (FIG. 2C) is fabricated in a way similar to the magneticfield sensor 24 of FIG. 1C. The different molded capsule 16′ has aregion, which, unlike the molded capsule 16 of FIGS. 1-1C, forms aninsulating layer 16 d′ proximate to the second opposing surface 12 bb ofthe die attach pad 12 b between the magnet 22 and the second opposingsurface 12 bb of the die attach pad 12 b. The insulating layer 16 d′ canhave a predetermined thickness to separate the magnet 22 from the secondsurface 12 bb of the die attach pad 12 b by a predetermined distance.

As shown, in some embodiments, the thickness of the insulating layer 16d′ is selected to be less, e.g., substantially less, than a combinedthickness of the die attach pad 12 b and the magnetic field sensorcircuit die 10.

The lead frame 12 includes leads 12 a′, which, unlike the leads 12 a ofFIG. 1 can have no bend, since the magnet 22 will not contact the leads12 a′, otherwise shorting them to the die attach pad 12 b.

As described above in conjunction with FIG, 1C, in some embodiments, themagnet 22 can be omitted and the liquid encapsulant 20 can be filledwith magnetic particles to form a permanent magnet or with soft magneticparticles to form a flux concentrator.

Referring now to FIG. 3, in which like elements of FIG. 1 are shownhaving like reference designations, another method of fabricating amagnetic field sensor includes attaching the magnetic field sensorcircuit die 10, i.e., a magnetic field sensing element, to the firstsurface 12 ba of the die attach pad 12 b of the lead frame 12. The dieattach pad 12 b has the first surface 12 ba and the second opposingsurface 12 bb. The method can also include coupling the magnetic fieldsensor circuit die 10 to the leads 12 a of the lead frame 12 with thewire bonds 14 or the like.

Referring now to FIG. 3A, in which like elements of FIG. 3 are shownhaving like reference designations, the method further includes forminga molded capsule 50 enclosing the magnetic field sensor circuit die 10.The molded capsule 50 can be made of a variety of materials, forexample, E670C mold compound from the Sumitomo Corporation, HYSOL® MG52Fmold compound from the Henkel Loctite Corporation, or PLASKON® CK-6100mold compound from Cookson Electronics. In some embodiments, the moldedcapsule 50 can be formed in a one step molding process. The moldedcapsule 50 covers the second surface 12 bb of the die attach pad 12 bforming an insulating layer 50 a over the second surface 12 bb of thedie attach pad 12 b.

Referring now to FIG. 3B, in which like elements of FIGS. 3 and 3A areshown having like reference designations, a magnet 52 can be placed overthe insulating layer 50 a. In some embodiments, an adhesive layer 54 isdisposed between the magnet 52 and the insulating layer 50 a. Theadhesive layer can be cured after the magnet 52 is disposed thereon. Theinsulating layer 50 a can have a predetermined thickness to separate themagnet 52 from the second surface 12 bb of the die attach pad 12 b by apredetermined distance.

Referring now to FIG. 3C, in which like elements of FIGS. 3-3B are shownhaving like reference designations, a molded enclosure 56 is formedsurrounding at least the magnet 52. In some embodiments, the moldedenclosure 56 can also surround or partially surround the molded capsule50.

As shown, in some embodiments, the thickness of the insulating layer 50a is selected to be less, e.g., substantially less, than a combinedthickness of the die attach pad 12 b and the magnetic field sensorcircuit die 10.

In some embodiments, the magnet 52 has a magnetic field orientedapproximately perpendicular to the first and second surfaces 12 ba, 12bb, respectively of the die attach pad 12 b. In these embodiments, themagnetic field sensor circuit die 10 comprises a magnetic field sensingelement, for example, a Hall effect element, having a maximum responseaxis also approximately perpendicular to the first and second surfaces12 ba, 12 bb of the die attach pad 12 b.

In some other embodiments, the magnet 52 has a magnetic field orientedapproximately parallel to the first and second surfaces 12 ba, 12 bb,respectively, of the die attach pad 12 b. In these embodiments, themagnetic field sensor circuit die 10 comprises a magnetic field sensingelement, for example, an anisotropic or giant magnetoresistance element,having a maximum response axis also approximately parallel to the firstand second surfaces 12 ba, 12 bb of the die attach pad 12 b.

The above-described method above results in a magnetic field sensor 58having the lead frame 12 with the die attach pad 12 b, the die attachpad 12 b having the first and second opposing surfaces 12 ba, 12 bb,respectively. The magnetic field sensor circuit die 10 is proximate tothe first surface 12 ba of the die attach pad 12 b. The molded capsule50 encloses the magnetic field sensor circuit die 10 and forms aninsulating layer 50 a over the second surface 12 bb of the die attachpad 12 b. The magnet 52 is proximate to the second surface 12 bb of thedie attach pad 12 b. The molded enclosure 56 surrounds at least themagnet 52.

In some other embodiments, similar to embodiments described above inconjunction with FIG. 1C, the magnet 52 can be omitted. In theseembodiments, the material of the molded enclosure 56 can be filledeither with magnetic particles to form a permanent magnet or with softmagnetic particles to form a flux concentrator. In these embodiments, itmay be advantageous to form the molded enclosure 56 on only one side ofthe lead frame 12, i.e., a side of the lead frame 12 opposite to themolded capsule 50.

Referring now to FIG. 4, in which like elements of FIGS. 3-3C are shownhaving like reference designations, a lead frame strip 60 includes aplurality of lead frames 62 a-62 f, each of which can be cut from thelead frame strip at a later time. Each one of the lead frames 62 a-62 fcan be the same as or similar to the lead frame 12 shown in FIGS. 1-1C,2-2C and 3-3C. Each one of the lead frames 62 a-62 f is shown at adifferent step in a manufacturing process.

The lead frames 62 a-62 f has the magnetic field sensor circuit die 10,i.e. the magnetic field sensing element, disposed over a first surface adie attach pad (not visible) of the lead frames 62 a-62 f. In theseviews, the magnetic field sensor circuit die 10 is over top of the dieattach pad.

Regarding the lead frames 62 b-62 f, the molded capsule 50 encloses themagnetic field sensor circuit die 10 and forms an insulating layer (notvisible) on the second surface (not visible) of the die attach pad (notvisible). Regarding the lead frames 62 c-62 f, the magnet 52 isproximate to the second surface (not visible) of the die attach pad notvisible). For the lead frames 62 c- and 62 e-62 f, the magnet 52 isunder the die attach pad. The lead frame 62 d is shown upside down fromthe others to more clearly show the magnet 52 as upward in this view.Regarding the lead frames 62 d-62 f, a capacitor 64 can be disposed onthe same side of the lead frame 62 d as the magnet 52, i.e., upward inthe view of lead frame 62 d. Regarding the lead frames 62 e-62 f, themolded enclosure 56 surrounds at least the magnet 52 to form themagnetic field sensor 58, but in some embodiments also surrounds themolded capsule 50 and/or the capacitor 64.

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described preferred embodiments of the invention, it will nowbecome apparent to one of ordinary skill in the art that otherembodiments incorporating their concepts may be used. It is felttherefore that these embodiments should not be limited to disclosedembodiments, but rather should be limited only by the spirit and scopeof the appended claims.

What is claimed is: 1-22. (canceled)
 23. A magnetic field sensor,comprising: a lead frame comprising a die attach pad, wherein the dieattach pad comprises first and second opposing surfaces; a magneticfield sensor circuit die coupled proximate to the first surface of thedie attach pad; a molded capsule comprised of a mold compound, themolded capsule enclosing the magnetic field sensor circuit die, whereinthe molded capsule covers the second surface of the die attach pad withthe mold compound, and wherein the mold compound of the molded capsuleforms an insulating layer over the second surface of the die attach pad,wherein a thickness of the insulating layer is less than a combinedthickness of the die attach pad and the magnetic field sensor circuitdie; a magnet coupled proximate to the second surface of the die attachpad so that the insulating layer is between the magnet and the secondsurface of the die attach pad; and a molded enclosure surrounding themagnet.
 24. The magnetic field sensor of claim 23, further comprising anadhesive material disposed between the magnet and the insulating layer.25. The magnetic field sensor of claim 23, wherein the molded enclosurealso surrounds the molded capsule.
 26. The magnetic field sensor ofclaim 23, wherein the molded capsule consists of one uniform material27. The magnetic field sensor of claim 23, further comprising a glassfilled epoxy disposed on the second surface of the die attach pad. 28.The magnetic field sensor of claim 23, further comprising a capacitorcoupled across at least two leads of the lead frame at a position thatresults in the capacitor being encased within the molded capsule. 29.The magnetic field sensor of claim 23, wherein the magnet has a magneticfield oriented approximately perpendicular to the first and secondsurfaces of the die attach pad, and wherein the magnetic field sensorcircuit die comprises a magnetic field sensing element having a maximumresponse axis approximately perpendicular to the first and secondsurfaces of the die attach pad.
 30. The magnetic field sensor of claim23, wherein the magnet has a magnetic field oriented approximatelyparallel to the first and second surfaces of the die attach pad, andwherein the magnetic field sensor circuit die comprises a magnetic fieldsensing element having a maximum response axis approximately parallel tothe first and second surfaces of the die attach pad. 31-33. (canceled)34. A magnetic field sensor, comprising: a lead frame comprising a dieattach pad, wherein the die attach pad comprises first and secondopposing surfaces; a magnetic field sensor circuit die coupled proximateto the first surface of the die attach pad; a molded capsule enclosingthe magnetic field sensor circuit die, wherein the molded capsule coversthe second surface of the die attach pad forming an insulating layerover the second surface of the die attach pad; and a first moldedstructure disposed proximate to the second surface of the die attachpad, wherein the first molded structure is filled with ferromagneticparticles to either generate a magnetic field or to concentrate amagnetic field, wherein the insulating layer formed from the moldcompound is disposed between the first molded structure filled withferromagnetic particles and the die attach pad; and a second moldedstructure enclosing the first molded structure, wherein the secondmolded structure is configured to retain the first molded structureproximate to the die attach pad.
 35. The magnetic field sensor of claim23, wherein the magnet comprises a solid magnet.
 36. The magnetic fieldsensor of claim 23, wherein the magnet comprises a mold compound filledwith ferromagnetic particles.
 37. The magnetic field sensor of claim 23,wherein the insulating layer comprises a substantially flat outersurface, forming a substantially flat surface upon which the magnet isdisposed, and wherein a surface of the magnet proximate to theinsulating layer is substantially flat.
 38. The magnetic field sensor ofclaim 34, wherein the second molded structure further encloses at leasta portion of the molded capsule.
 39. The magnetic field sensor of claim34, wherein a surface between the molded capsule and the first moldedstructure is substantially flat throughout the surface.
 40. The magneticfield sensor of claim 34, wherein a thickness of the insulating layer isless than a combined thickness of the die attach pad and the magneticfield sensor circuit die.